The SI unit for energy is Joules (J). One joule is equal to 1kg*m^2*s^-2. A kilo-joule (kJ) is equal to 1000 joules of energy. Calorie (Cal) is used to denote energy stored inside the food or energy used by the body. 1 Cal is equal to 4.184 Joules. Similarly, a kilo-calorie (KCal) is equal to 1000 calories.
Atkinds, Peter. Physical Chemistry. 9th. Oxford University Press, 2009. Print.